Thousands of Turkish troops poured into northern Iraq in pursuit of separatist Kurdish rebels today in Ankara’s biggest cross-border ground incursion in more than a decade.

The Turkish military said thousands more soldiers were waiting at the border, ready to bolster an operation targeting rebels of the Turkish Kurd group, the Kurdistan Workers Party (PKK), which launches attacks on Turkey from bases in Kurdish-controlled northern Iraq.

Recep Tayyip Erdogan, the Turkish Prime Minister, said that he had informed President Bush and Nouri al-Maliki, the Iraqi Prime Minister, last night, when the attack started.

"We will withdraw our troops once the mission is complete and within the shortest possible time,'' he told reporters. He promised that all care would be taken to avoid civilian casualties. “We respect the territorial integrity of Iraq.''

Showing pictures of soldiers walking through snowy mountain paths with helicopters overhead, Turkish television and newspaper websites saidthat up to 10,000 troops led by ten generals had crossed the porous border into northern Iraq in a bid to lay waste to the PKK’s mountain lairs and logistics. CNN Turk said 3,000 special forces took part.

The operation is apparently timed to prevent them regrouping after a cold winter of inaction to launch fresh attacks, as they regularly do in spring. It also comes after months of increased co-operation with the United States, which has been giving intelligence information to help Turkey launch air attacks on rebel bases.

Turkish media have been reporting a growing rift between the US-backed Iraqi administration and Massoud Barzani, the Kurdish leader who controls northern Iraq.

The incursion attracted criticism from foreign capitals, but the generally muted language of protest, especially from Washington, was seen here as proof that Turkey’s move had the tacit backing of the United States.

“A land operation is obviously a whole new level,” the Deputy Assistant Secretary of State Matthew Bryza told reporters in Brussels, saying that this was “not the greatest news”. He said that until now Turkey and the United States had been co-operating fully on a campaign of pinpoint attacks that minimised damage to civilians and property.

Rear Admiral Admiral Gregory Smith, the US military spokesman, said that the United States continued to support Turkey’s right to defend itself and was aware of the operation: “Multi-National Forces-Iraq is aware Turkish ground forces have entered into northern Iraq, for what we understand is an operation of limited duration to specifically target PKK terrorists in that region. Turkey has given its assurances it will do everything possible to avoid collateral damage to innocent civilians or Kurdish infrastructure.”

“Contrary to the belief among the Turkish general public, the United States is not against a land operation, but it does not want a full scale, uncontrolled operation conducted without cooperation,” said Sedat Laciner, head of the Turkey-based International Strategic Research Institute. He said the details will have been discussed with US generals in advance.

“To get the support of the international community is very important not only for the success of the operation but also to demoralise the PKK members and show them that they are isolated,” said retired ambassador and analyst Yalim Eralp.

Turkey’s parliament had given the go-ahead for the attack in October under great public pressure for action following a deadly PKK ambush on a group of young Turkish conscripts. Publicly belligerent but privately reluctant given the international repercussions of a unilateral strike, Mr Erdogan, engaged in heated diplomacy with a US administration wary of any invasion of the only stable part of post-Saddam Iraqi territory. After the deal on intelligence cooperation, Turkish warplanes hit PKK bases in northern Iraq and engaged in “hot pursuit” border operations against fleeing rebels, but the momentum for a large-scale land invasion began to build early this year.

Turkey has launched several incursions across the border into northern Iraq since the early 1980s, when the PKK first came into being, but none of them did lasting damage – not even two invasions in 1995 and 1997 involving tens of thousands of troops. Often the rebels would notice a lengthy build up and flee further into Iraq or back into Turkey. This time, Turks hope that an earlier-than expected spring operation with more specialist troops and equipment could steal a march on the guerrillas, who would have expected them to wait until the weather cleared. This way the rebels are also deprived of spring foliage to give them cover.

“The special forces unit is important here -- with its equipment and logistics support, it has much greater mobility in winter than the terrorists, who have nowhere to run in this weather,” said Mr Eralp. “If they had waited for spring the PKK would have been more mobile and the soldiers would have been at a disadvantage.”

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